1. Field of the Invention
The present invention relates to novel gel-forming compositions comprised of alkali metal silicates, and, more especially, to microemulsions thereof.
The present invention also relates to the use of said microemulsions for soil stabilization purposes and for the plugging of geological surface and subterranean ground formations.
2. Description of the Prior Art
It is known to this art that by addition of certain organic reagents to alkaline silicates, it is possible to obtain silica gels capable of conversion into a coherent and hard mass having the properties of a cement. Among the recommended reagents, notable are the organic esters which hydrolyze in the presence of silicates and release an acid compound to form a gel that is impermeable to water. Diacid esters particularly suitable for the sealing and consolidation of soils are described in U.S. Pat. No. 3,493,406. The selection of a particular ester or esters may depend upon the gelling time desired, in view of the intended application, and thus on the speed of hydrolysis of the esters under the temperatures likely to be encountered.
However, certain esters have the disadvantage of being poorly soluble in water, which mandates vigorous agitation prior to injection in order to provide a homogeneous mixture which gels uniformly.
The use of silicates to reduce or eliminate the permeability of subterranean formations in the treatment of oil and gas wells is also known to this art. Permanent or temporary plugging or clogging processes are used, particularly, in the drilling, reconditioning, completion and stimulation of wells and in tertiary recovery processing. Silicates have been suggested, for example, as additives to mixtures of cement or resins to seal zones characterized by high loss of circulation during drilling, or to prevent communication between several layers of the reservoir in the cementing of "casings". Silicates are also used in fracturation to obtain viscous gels having thixotropic properties. In these techniques, the silicates are employed essentially as additives and without a gel-forming reagent. In the gel form, the silicates are used in tertiary recovery operations in order to plug zones of high permeability, to prevent excessive intrusions of water into producing wells. The silicate gels heretofore employed in the petroleum industry are intended to form permanent seals. However, the injection of an alkaline silicate solution, or emulsion, into a porous medium poses certain difficulties: slow propagation, and the risk of separation which would give rise to heterogeneous clogging. If it is desired to obtain temporary and reversible clogging according to the known state of the art, organic polymers are used. These processes have the disadvantages in that they are uncertain with respect to their behavior under a variety of temperatures and the duration of the seals; furthermore, destruction of the polymer gel is often difficult to control, as is the provision of residual permeabilities less than the initial permeabilities.